Genetic Testing During Pregnancy – What It Is, Benefits, Risks & Options

You may have to undergo various tests and screenings during pregnancy to ensure your baby’s well-being. Sometimes parents may be advised to undergo genetic testing in pregnancy, which may be performed to rule out any risk of genetic abnormalities an unborn baby could inherit. Screening genetic factors early on in the pregnancy helps doctors and couples stay ahead of any potential complications and make plans for care and support during and after pregnancy.

What Is Genetic Testing?

Genetic testing involves testing the blood of both parents to look for abnormal genes, which the parents may pass on to their baby. In case one of the parents has abnormal genes, there may not be any genetic complications. In case both parents have an abnormality in their genes, even then, there is only a 25% chance that your baby may have faulty genes too (1).

When Is Genetic Testing Ideally Done in Pregnancy?

It is recommended that genetic testing be done before you plan to get pregnant. And where the pregnancy may be unplanned, it is recommended that you opt for genetic counselling at the earliest.

Why Is This Testing Recommended?

You may be advised genetic baby testing or genetic foetal testing by your doctor because of any of the following reasons (2):

• If you are a woman who has had two or more than two miscarriages. Sometimes, certain chromosomal deformities in the foetus may lead to a spontaneous miscarriage.
• If you, your partner or a close relative has some kind of genetic disorder.
• If you already have a child who is suffering from birth defects (due to genetic reasons).
• If you are an older woman, 35 years or older, then genetic testing for pregnancy over 35 may be recommended.
• If you have had a stillbirth with your baby having prominent physical signs of a genetic illness.
• If the prenatal screening results were abnormal.

These are some of the reasons why your doctor may recommend that you go in for genetic testing.

What Are Common Genetic Diseases

Here are some common genetic diseases that may occur due to faulty or deformed genes (3):

1. Thalassemia

Thalassemia is a blood disorder which may lead to complications like anaemia, liver ailments or problems in bone growth. In some cases, if a baby has this genetic disorder, he may not even survive (4).

2. Cystic Fibrosis

Cystic fibrosis is a fatal genetic condition that may cause life-threatening complications in your baby. It may cause severe digestive problems or may even lead to lung damage (5).

3. Sickle Cell Disease

This genetic problem may lead to various health complications such as anaemia, weakened immune system, etc.

4. Fragile X Syndrome

This may lead to mental retardation, learning disabilities and developmental complications in your child.

5. Tay-Sachs Disease

This genetic disorder adversely affects the nervous system of your baby and thus may lead to various problems of the nervous system, especially during early childhood.

6. Duchenne Muscular Dystrophy

This genetic disorder becomes prominent before your child begins his formal education, which is around 6 years of age. This may lead to weaker muscles and may also cause fatigue; it may progress from the legs to the upper part of the body.

Main Types of Prenatal Genetic Tests Performed During Pregnancy

You may wonder what genetic testing is done during pregnancy. Well, there are two main tests that your doctor may recommend: screening tests and diagnostic tests. Here is more information on how these prenatal genetic tests may be performed during pregnancy to check for any genetic glitches:

1. Screening Tests

The screening tests may tell if you have a baby with genetic ailments .

a. First Trimester Combined Screening Test

Genetic testing during pregnancy first trimester is done through blood tests during your 10 to 12 weeks of pregnancy, which may also include an ultrasound at around 11 to 13 weeks of pregnancy (6). The results of both these tests may help in establishing the risk of trisomy 21 (Down syndrome) or trisomy 18 (7). However, the tests do not tell whether or not your baby may have these ailments.

b. Maternal Serum Screening

For genetic testing during pregnancy second trimester, a blood test may be conducted around 15 to 20 weeks of pregnancy to establish the risk of neural birth defects (spina bifida), Down syndrome or trisomy 18. In case you are at risk, you may be recommended to go for further tests.

2. Diagnostic Tests

The diagnostic tests may tell you about the defects that your baby may have (3).

a. Chorionic Villus Sampling (CVS) (11 to 13 weeks)

This test involves taking a sample of the placenta and testing it for any genetic diseases such as cystic fibrosis, Down syndrome and others. In some rare cases, a woman may have a miscarriage due to this test, though the chances are only 1 in a hundred (8).

b. Amniocentesis (15 to 19 weeks)

This test involves testing the amniotic fluid to check for any genetic disorders, such as Down syndrome and others. Sometimes this test may lead to a miscarriage, though the chances are very minimal (1 in every 200 cases).

c. Ultrasound Scans (18 to 20 weeks)

This test may be done at a bit later stage in pregnancy to identify structural and physical abnormalities, limb defects, heart abnormalities and spina bifida.

What Do the Results of Prenatal Genetic Testing Mean?

The test results of the prenatal genetic testing can be positive or negative. If the test results are positive, this means that your baby may be at a higher risk of having various genetic abnormalities, but that does not mean that your baby will definitely have them. On the other hand, if the test results are negative, then it means that your baby has low chances of having any genetic diseases; however, it does not entirely rule out the possibility.

The genetic testing that involves amniocentesis or Chorionic Villus Sampling may give you more comprehensive and definite results in comparison to other testing methods. After your test results, your doctor may guide you to seek the help of a genetic counsellor to understand your case and also on the further course of action.

How Accurate Are These Genetic Screening Tests?

Just like the possibility of any test results going faulty, there are chances that genetic screening tests may show faulty results too. If the test results are positive but there is no problem, then it is called false-positive test results. Whereas, if the test results are negative but there is a problem, then it is called false-negative test results. You may get in touch with your doctor to know more about your test results and their authenticity.

Are There Any Risks of Genetic Testing While Pregnant?

Pregnancy may make you sceptical because everything that you do may have an impact on your baby as well. So, are there any genetic testing pros and cons that you should know about? The first and foremost thing to understand is that genetic testing is a personal choice. So, if you are thinking whether or not genetic counselling has any risk, the answer is that it may have more emotional stress than physical stress. It can be extremely disheartening and difficult to know that you may have a baby with a genetic disorder, which may adversely affect your child’s life.

Also, the screening tests only tell you whether you are at risk of having a baby with a genetic disorder, and to know the defects, you will have to undergo diagnostic tests. Where some parents may want to know about a genetic disorder to prepare better for their baby, on the other hand, others may want to know to terminate the pregnancy. However, there are some parents who do not want to know whether or not their baby may have any genetic disorder. It is entirely up to you as a parent to decide whether you want to go for genetic counselling or not.

Questions to Discuss With Your Doctor About Pregnancy Genetic Testing

Questions like which screening tests you should get or what your test results could mean are likely to come, and you are not alone in having those questions. So, don’t be afraid to ask questions and talk in detail with your obstetrician. Here, let us help you with common questions related to genetic test during pregnancy that you can discuss with your doctor:

• What kind of screening tests would you recommend basis my health history?
• What are the risks and benefits of each type of test you recommend?
• If the screening test results are positive, what will be the next steps?
• Is there any chance of false positives in prenatal genetic testing?

FAQs

1. What conditions can genetic testing during pregnancy detect?

Prenatal genetic testing can detect conditions, like spinal muscular atrophy (SMA), Down syndrome, and DiGeorge syndrome (a condition with missing pieces of chromosomes).

2. Who is recommended for genetic testing?

Getting genetic testing during pregnancy is a voluntary choice. Doctors can recommend the testing options, and if you are okay with it, you can consult further with your doctor and get the tests done. Nonetheless, your doctor may recommend genetic testing during pregnancy if you have received an irregular result of a genetic screening test, there is a family history of genetic conditions, you have conceived over the age of 35, or have a history of stillbirth or miscarriage (9).

3. How accurate is genetic testing done during pregnancy?

Screening tests (non-invasive prenatal testing (NIPT), although high but not 100%) (10) are comparatively less accurate than diagnostic tests (amniocentesis or CVS), which are usually more accurate, with over 99% accuracy. It is wise to discuss the results of the genetic tests with your doctor and discuss what needs to be done further.

4.  Are there risks to genetic testing during pregnancy?

Also Read:

Sequential Test while Pregnant
Double Marker Test during Pregnancy
Triple Marker Test in Pregnancy
Quadruple Marker Test During Pregnancy
Common Trimester Wise Test in Pregnancy

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Sources References

1. Mayo Clinic – Prenatal testing: Is it right for me?

2. ACOG – 3 Questions to Ask Yourself Before Getting Prenatal Genetic Testing

3. Cedars Sinai – What Happens During Genetic Testing in Pregnancy

4. Mayo Clinic – Thalassemia

5. Mayo Clinic – Cystic fibrosis

6. NSW Government – Screening Tests During Pregnancy 

7. The Women’s – Genetic testing in pregnancy

8. NSW Government – Diagnostic Tests During Pregnancy

9. Cleveland Clinic – Prenatal Genetic Testing

10. NSW Government – NON-INVASIVE PRENATAL TESTING (NIPT)